docs: def to_bytearray(self):
          """
          Convert this frame into its bytearray representation.
  
          :return: bytearray representation of this frame.
          """
          header = bytearray(struct.pack(
              '>HHHBB',
              self.transaction_id,
              self.protocol_id,
              self.length,
              self.unit_id,
              self.fcode
          ))
          return header + self.data